Present-day systems use masks with a soft pellicle, a soft pellicle not influencing the beam path. An AIMS device in which masks with a soft pellicle are examined with regard to their quality need not permit the pellicle to be incorporated into the considerations. If an exposure source with 157 nm technology is used, a hard pellicle is necessary in order to withstand the radiation loading with the transmission properties remaining the same. However, a hard pellicle, as an additional glass plate in the beam path leads to imaging errors or aberrations of the lens.
Hitherto, an AIMS device has been provided with two different imaging lenses having imaging properties optimized for the respective mask, i.e. with or without a hard pellicle. Rapid checking of the optical imaging properties of a mask, i.e. the corresponding aerial image of the mask, without a pellicle under real conditions in a stepper, i.e. as if a hard pellicle were present, is not possible with a known AIMS device. In this case, it would be necessary firstly to mount a pellicle onto the mask, which pellicle, in the event of a defect occurring in the mask, would have to be demounted for a corresponding repair of the mask and be mounted again for subsequent checking of the repaired mask. This means an additional expenditure of time. It is nevertheless necessary to be able to examine the masks both with and without a hard pellicle.